1. Technical Field
The present invention relates to a stress sensing device adapted to sense both shear force acting in a shear direction and pressing force acting in a direction perpendicular to a shear direction; to a tactile sensor furnished with this stress sensing device; and to a grasping apparatus furnished with this tactile sensor.
2. Related Art
Grasping apparatus designed to grasp and pick up objects of unknown weight or coefficient of friction by a robot arm, a robot hand, a robot manipulator or the like are known in the art. In a grasping apparatus of this kind, in order to grasp an object without breaking it and without letting the object slip and drop, it is necessary to sense force acting in the direction perpendicular to a grasped face (pressing force), as well as force acting in the planar direction (shear direction) of the grasped face (shear force). Sensors adapted to sense such forces are known in the art (see Japanese Laid-Open Patent Application 2006-208248, for example).
The tactile sensor disclosed in Japanese Laid-Open Patent Application 2006-208248 has structures of cantilever construction extending from the edge of an opening provided to the sensor substrate. Each of these structures is composed of a sensing portion of flat plate shape, and a hinge portion linking the sensing portion with the sensor substrate. A conductive magnetic film is formed in the sensing portion of this structure and a piezoresistive film is formed in the hinge portion, with the conductive magnetic film and the piezoresistive film having electrical continuity. Additionally, an electrode is disposed in the hinge portion, providing a configuration whereby electrical current, generated by piezoresistance of the hinge portion when the hinge portion bends due to pressure, flows from the electrode. The tactile sensor has a plurality of structures like those described above formed on the sensor substrate, with some of these structures oriented upright with respect to the sensor substrate, while others are held parallel to the sensor substrate. An elastomer is disposed on the sensor substrate, and the upright structures are embedded into the elastomer. Shear force can be measured by the upright structures, while pressing force can be measured by the structures parallel to the substrate face. With this tactile sensor, shear force is sensed by the structures that are upright with respect to the sensor substrate, and pressing force is sensed by the structures that are held parallel to the sensor substrate.